Securing an implantable medical device in position while reducing perforations

ABSTRACT

Methods and systems of making a medical electrical lead type having a set of tines. A system for implantation of a lead medical electrical lead in contact with heart tissue, comprises an elongated lead body; a set of curved tines mounted to and extending from a distal end of the lead body, the tines having a length (dD) and an effective cross sectional area, and a delivery catheter. The delivery catheter encloses the lead body and has a distal capsule portion enclosing the tines. The tines exerting a spring force against the capsule and provide a stored potential energy. The delivery catheter has an elastic, not stiff and low column strength ejection means for advancing the lead and tines distally from the capsule and fixating the tines within the heart tissue, the controllable and the stored potential energy of the tines together provide a deployment energy. The tines when so fixated in the tissue provide a fixation energy. The deployment energy and the fixation energy of the tines are equivalent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/160,710, filed on May 13, 2015. The disclosure of the aboveapplication is incorporated herein by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to implantable medical devices such as medicalelectrical leads. More particularly, the present disclosure relates to amedical electrical lead with a set of tines that are configured tosecurely attach to tissue without perforating the heart wall.

BACKGROUND

Medical electrical leads are configured for pacing, sensing,cardioversion, and defibrillation therapies. Leads attach to tissuethrough active fixation (e.g. tines etc.) or passive fixation (e.g.adhesive). Exemplary medical electrical devices with tines, comprisingnickel titanium (Nitinol), are known in the art, as shown and describedin U.S. Pat. No. 4,505,767 to Quinn, U.S. Pat. No. 5,067,957 to Jervis,U.S. Pat. No. 7,650,186 to Hastings et al. and US Pregrant PublicationNo. 2012-0172892 A1 filed Apr. 28, 2011 to Grubac et al. Delivery oftherapy is dependent upon the lead tines staying attached to the cardiactissue. Occasionally, a lead can dislodge from its position which isproblematic since therapy cannot be delivered to the tissue. Lead tinescan be designed to be securely attached to tissue in a manner that thelead will not dislodge; however, perforations of the heart wall canincrease. Perforations occur when tines completely pierce or penetratethe heart wall that comprises three layers—endocardium, myocardium andepicardium. Each heart wall layer possesses different tissue properties.For example, the epicardium is harder than the thicker softer myocardiumwhile the myocardium is softer than the endocardium. Since each heartwall layer possesses different tissue properties, tines pass througheach layer at a different rate of speed. Consequently, reduceddislodgement of tines must be balanced against reduction of perforationsby tines.

Typically, to address this issue, lead tines have been designed basedupon a push force applied by user that is translated to the tines. It isdesirable to develop tines, on a medical device, that does not merelyrely on the force applied by the tines but rather eliminatesdislodgement while substantially reducing perforations during implantingof a medical device.

SUMMARY

The present disclosure is directed to a medical electrical lead havingset of tines that eliminates unintended dislodgements from tissue.Energy stored in the tines is released when the delivery system isretracted. Retracting the delivery system controls the penetration ofthe set of tines into the cardiac tissue (i.e. myocardium).

The set of tines are configured to satisfy pre-specified conditions. Forexample, tines must be easily deployed and attached to various types ofcardiac tissue (e.g. endocardium, myocardium and epicardium) whileensuring adequate fixation occurs to avoid dislodgment of the tines fromthe tissue. Additionally, the tines are required to hold the electrodein contact with the myocardium to maintain low stable pacing thresholds.Moreover, the tines must be able to be easily removed with minimaldamage to the myocardium, in order to facilitate device repositioning,retrieval and extraction. Device repositioning typically occurs toachieve a more optimal pacing location. Retrieval and extraction mayoccur when a healthcare professional (e.g. physician) determines thatthe implantable medical device (IMD) needs to be replaced with anotherIMD.

One or more embodiments relate to configuring a crown with a set oftines extending therefrom in which the crown is secured (e.g. snap-fit,adhesive) to any medical electrical lead. The set of tines areconfigured by using a set of transfer functions. The first transferfunction is directed to tissue penetration by the tines. The tissuepenetration transfer function relates an effective cross-sectional areaof the fixation mechanism (e.g. fixated tine etc.) at retraction to theeffective cross-sectional area of the fixation mechanism (e.g. tineetc.) at the point of deployment of the tine(s). Specifically, theeffective cross-sectional area of the fixation mechanism (e.g. fixatedtine etc.) at retraction is configured to be larger than the effectivecross-sectional area of the fixation mechanism (e.g. tine etc.) at thepoint of deployment of the tine(s).

The second transfer function configures tines in a manner that allowsthe tines to be safely removed from the myocardium. To ensure the tinescan be safely removed, the second transfer function relates penetrationenergy and surface area. The tissue penetration energy at a surface areaequivalent to the inside surface area 48 a of the tine (FIG. 8) comparedto the holding energy of the tines upon retraction to determine if thetines would damage tissue upon retraction. Holding energy (WintgR) isdeployment work/energy of the retraction portion of a full cycle test.

The second transfer function associates maximum peak force of deploymentand retraction to occur at substantially equivalent displacements of thetine cycle. A full tine cycle is shown from FIGS. 3A-3D in which thetines enter and attach to cardiac tissue.

One or more other embodiments relates to a method of making a medicalelectrical lead type having a set of tines. The method comprisesdetermining an effective cross-sectional area characteristic of a distalend of each tine in the set of tines relative to a displacement energyrequired to displace a cardiac tissue layers. In response to determiningthe effective cross-sectional area characteristic of the distal end ofeach tine, a determination is made as to whether a substantially highconfidence level (e.g. 95% or more) characteristic exists thatperforation of the hear wall is avoided. The set of tines are made suchthat each tine exhibits the determined characteristics (i.e.cross-sectional area characteristic of a distal end of each tine, and asubstantially high confidence level characteristic exists thatperforation is avoided).

One or more other embodiments relate to dislodgement of the set of tines(i.e. nitinol tines), which behave in a manner similar to springs. Inthis embodiment, the lead tip is typically pulled and/or displaced morethan about 50% the length of the tine, which is typically above a forcethreshold in order to cause dislodgement. Force threshold is the minimalamount of force required to dislodge one or more tines from the tissue.In another embodiment, the tine tip is moved 90 degrees from itsoriginal position to cause dislodgement. Any force, applied to the leadthat does not result in dislodgement, will not affect the pacingthreshold since the tines automatically spring back into their originalposition.

The details of one or more aspects of the disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the disclosure will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a lead in the process of implantationand an associated device system for obtaining the parameters to bemeasured and for providing an indication of the fixation of tines thathave entered heart tissue.

FIG. 2 is a flow chart illustrating a first embodiment of the analyticalmethod performed by the device system of FIG. 1.

FIG. 3A is a schematic diagram depicting pre-deployment of the set oftines occurring such that the lead and tines are retracted in thedelivery catheter and the delivery catheter is placed against themyocardium.

FIG. 3B is a schematic diagram depicting during the initial stage of thedeployment, the tines are immediately positioned at an angle as soon astines exit the catheter and start penetrating tissue.

FIG. 3C is a schematic diagram that shows during the middle of thedeployment sequence, the majority of the surface area of tines isprojected in front of the lead, even before the lead body touchestissue.

FIG. 3D is a schematic diagram that shows after full deployment of thelead such that the lead tip is touching or in contact with tissue, andthe surface area of the fully deployed tines prevents any acute orchronic migration of the lead body.

FIG. 4 is a flow chart illustrating a method of determiningcharacteristics of a set of tines employing an analytical methodaccording to the invention.

FIG. 5 depicts a schematic view of a medical electrical lead with a setof tines at a distal end of the lead.

FIG. 6 depicts a schematic and cross-sectional view along a longitudinalaxis defined by lines 5-5 of a distal end of medical electrical leadwith a set of tines at a distal end of the lead.

FIG. 7 depicts a schematic and cross-sectional view along a longitudinalaxis defined by lines 5-5 of a medical electrical lead body.

FIG. 8 depicts a schematic view of a medical electrical lead with a setof tines at a distal end of the lead.

FIG. 9 depicts a schematic and cross-sectional view along a longitudinalaxis defined by lines 8-8 of a medical electrical lead with a set oftines at a distal end of the lead.

FIG. 10 is a flow diagram depicting a method of making a lead withtines.

FIG. 11A depicts a schematic view of the initial implant stage in whichthe delivery system including the lead is positioned near the rightatrial appendage (RAA) while the tines are retracted to avoid snaggingthe tines on any anatomical areas.

FIG. 11B depicts a schematic view of the delivery system is placed orpushed in the appendage in the desired target location.

FIG. 11C depicts a schematic view of the delivery system during theprocess of deploying the tines.

FIG. 11D depicts a schematic view of the delivery system moving in aproximal position thereby causing tines to contact the epicardialsurface.

FIG. 12A depicts a schematic view of the delivery system in which thedelivery system is flexible as shown by a bend and angle in the deliverysystem.

FIG. 12B depicts a lead attached to tissue.

FIG. 13A depicts a straight section of the tine-tissue interface duringinitial penetration of the endocardial surface

FIG. 13B depicts a straight section of the tine-tissue interface afterinitial penetration of the endocardial surface.

FIG. 13C depicts a straight section of the tine-tissue interface inwhich greater force is applied to the tine.

FIG. 13D depicts a straight section of the tine-tissue interface inwhich the tine has fully penetrated the tissue.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following detailed description of illustrative embodiments,reference is made to the accompanying figures of the drawing which forma part hereof, and in which are shown, by way of illustration, specificembodiments which may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from (e.g., still falling within) the scope of the disclosurepresented hereby.

Exemplary systems, methods, and interfaces shall be described withreference to FIGS. 1-13. It will be apparent to one skilled in the artthat elements or processes from one embodiment may be used incombination with elements or processes of the other embodiments, andthat the possible embodiments of such methods, apparatus, and systemsusing combinations of features set forth herein is not limited to thespecific embodiments shown in the Figures and/or described herein.Further, it will be recognized that the embodiments described herein mayinclude many elements that are not necessarily shown to scale. Stillfurther, it will be recognized that timing of the processes and the sizeand shape of various elements herein may be modified but still fallwithin the scope of the present disclosure, although certain timings,one or more shapes and/or sizes, or types of elements, may beadvantageous over others.

FIG. 1 illustrates a patient's heart 10, with a lead 22, introduced intothe left ventricle 12 by means of an introducer catheter 20. The lead issubsequently connected to an implantable medical device (IMD). IMDrefers to a pacemaker, an implantable cardioverter-defribrillator (ICD),a leadless pacemaker device (e.g. Micra®) or other implantable therapydelivery assembly configured to deliver electrical stimulation. The lead22 is introduced into or onto the left ventricle by means of an atrialtrans-septal puncture allowing the introducer catheter to enter the leftatrium 16. The lead 22 is then moved onto the left ventricle 12. Aventricular trans-septal puncture may also be employed. Tines 24 areshown extending from the distal end of lead 22 and adjacent the wall ofthe left ventricle 12. A single tine is a NiTi tension cantileverspring.

Exemplary tines 24 are shown and described in an article published bythe inventors of the present disclosure, the citation of which isMichael D. Eggen et al., Design and Evaluation of A Novel FixationMechanism for a Transcatheter Pacemaker, IEEE TRANSACTIONS ON BIOMEDICALENGINEERING, vol. 62, No. 9, (Sep. 9, 2015), the entire disclosure isincorporated herein by reference in its entirety.

In other embodiments, the lead 22 may be placed in other locations,including the atria (i.e. right, left) and/or the right ventricle. Thespecific relationships between the measured parameters and the tines mayvary with lead configuration and location. Correspondingly, the measuredparameters indicative of proper fixation may also vary.

The lead 22 is coupled by lead conductors - to an interface device 26such as a Medtronic Model 2290 Pacing Systems Analyzer (PSA). Theinterface device 26 is used to make the measurements of the parametersand provides the measurements to the computer 28. In some embodiments,the collection of the measured parameters may be done under physiciancontrol when determining a location to implant a lead 22. In otherembodiments, collection of the parameters may be done under control ofcomputer 28 or under control of software resident in the interfacedevice 26. The computer 28 employs the analytical methodology of thepresent invention to derive measurements and provide it to the outputdevice, which may be a conventional display. The analytical techniquesof the present invention, as discussed below, may be embodied in storedsoftware as executed by computer 28.

FIG. 2 is a flow chart illustrating operation of a first embodimentdeployment technique according to the present disclosure. At blocks 200,202, 204, 206, the computer 28 (FIG. 1) receives the input measuredparameters from the interface device 26. Method 200, shown relative toFIGS. 3A-3D, depicts sequential steps of tine deployment and tissueattachment relative to FIG. 2. In particular, method 200 discloses thesteps of the deployment sequence as to how the tines come out first andincrease the frontal area during deployment, in order to reduce leadbody perforation. At block 202 (FIG. 3A), pre-deployment occurs suchthat the lead 22 and tines 24 are retracted in the delivery catheter 20and the delivery catheter 20 is placed against the myocardium. Anexemplary delivery catheter may be the Attain® Deflectable CatheterDelivery System (Model number 6227DEF) commercially available fromMedtronic, Inc., the manual of which is incorporated herein by referencein its entirety. The catheter kit comes with a dilator, which is aninner catheter to transition from a guidewire to the catheter. The innerdiameter of the deflectable catheter is 7.2 French (2.4 mm). The innerdiameter of the dilator is 7 French (2.3 mm). The length of the dilatoris 60 cm. Any catheter less than 7.2 French will pass through thedeflectable catheter. Skilled artisans appreciate any type of deliverycatheter may be employed to deliver a lead to cardiac tissue.

At block 204 (FIG. 3B), during the initial stage of the deployment, thetines 24 are immediately positioned at an angle as soon as tines 24 exitthe catheter 20 and start penetrating tissue. This angle increases thefrontal surface area of the tine 24 resisting lead body motion, whileanchoring the tines 24 in the tissue. At block 206 (FIG. 3C), during themiddle of the deployment sequence, the majority of the surface area oftines 24 is projected in front of the lead 22, even before the lead bodytouches tissue. At block 208 (FIG. 3D), after full deployment of thelead 22, the lead tip is touching or in contact with tissue, and thesurface area of the fully deployed tines prevents any acute or chronicmigration of the lead body.

In one or more embodiments, the set of times are solely configured topenetrate viable cardiac tissue and cannot penetrate poor substrates(e.g. scar tissue), arteries, or veins. If the location is suitable forcardiac pacing and sensing, based upon measured response from cardiactissue, the physician may leave the lead 22 in place. In one or moreembodiments, the physician may re-position the lead 22 at anotherlocation, and the analytical process is re-started as described above.

Prior to implant, the tines are straightened by the delivery tool 20 sothat the tines point distally with respect to the device. The lead tinesare aligned to have their tips contact heart tissue and stores potentialenergy needed during implant to fixate (i.e., penetrate). Sharp tips onthe tine reduces the amount of energy needed to implant the device butit would also reduce the amount of force needed to damage tissue duringremoval. For this reason, the tine tip and the tine sides, shown ingreater detail with respect to FIG. 13, must be curved so that no sharpcorner is in contact with the tissue during removal.

Since the tines are curved, an exact cross-sectional area of the tine isdifficult to specify. Furthermore, the amount of force needed by thetines to fixate to the tissue will depend on the surface area of thetissue that is in contact with the tine. The amount of surface area ofthe tissue that is in contact with the tine is based on the surface areaof the distal end of the tine.

Safety features of the design are based on the retractioncharacteristics of the fixation mechanism. Performance features arebased on deployment characteristics of the fixation mechanism. Bydesign, safety and performance features are governed by delivery toolwork and/or energy input (i.e. offset) that is controlled by operator bytactile feedback. Tactile feedback is the response sensed by the userwhen moving the delivery system in position and/or placing the lead.Work/energy (Wintg (J)) is the area under the force-displacement curveof the penetration.

At the time of implant, the compound force of the tine spring (FmaxD)and the delivery tool capsule ejection acts on the effectivecross-sectional area of the tine over the tine length 38 needed to imbedinto the tissue (dD). dD involves deployment displacement of the fullcycle test.

The sum of potential energy of the fixation stored in the tine springand delivery tool capsule ejection mechanism can be important, in one ormore embodiments, for balancing the need to fixate reliably and theability to reposition the device when needed with minimum damage to thetissue. Potential fixation energy of the tine at deployment(WingtgDFmax) is only about 34% of the fixation energy of the tine atretraction (WingtgRFmax). WingtgDFmax (Maximum force at deployment) isthe potential fixation energy of the tine at deployment defined by theend of the force plateau (i.e. typically maximum peak force) and thedisplacement needed to reach the end of the force plateau. WingtgRFmaxis the potential fixation energy of the tine at retraction defined bythe end of the force plateau (i.e. typically maximum peak force) and thedisplacement needed to reach the end of the force plateau.

The amount of energy provided by the delivery tool capsule ejectionmechanism (or pushing on the lead) can be defined as the offsetdifference in energy needed to equal fixation potential energy ofdeployment to the fixation energy of the retraction.

Making deployment potential energy essentially equivalent to theretraction potential energy allows the design to maintain high reliablyof fixation within the use conditions defined by the tissue propertieswhile also permitting the design to be safely repositionable. The amountof energy needed to fixate is proportional to the effectivecross-sectional area of the penetrator. The penetrator, similar to atine, is used to during testing with tissue. The amount of energy neededto fixate is primarily determined by the properties of the endocardiallayer of the heart wall.

The amount of energy needed to retract the fixation mechanism issignificantly impacted by the properties of the epicardial layer of theheart wall. The determination that the epicardial layer affects theamount of energy needed to retract the fixation mechanism was based on acomparison of work/energy needed to tent the tissue under penetrationtests. Penetration occurs when an object enters the heart wall but doesnot go completely through it.

Reviewing tissue penetration data, it was observed that significantlymore work and/or energy is needed to dome the tissue from the epicardialsurface (i.e. inside/out) than endocardial surface (i.e. outside/in) upto a penetration point with the equivalent penetrator. Inside/out (IO)penetration is penetration moving from the endocardium to theepicardium. Outside/in (OI) penetration is penetration moving from theepicardium to the endocardium.

The effective length of the tine (dR or dD) is optimized by design to bein the range of the low limit point and the high limit point of the I/Oand O/I tissue population of the displacement. A low limit point is apoint at which there is the largest difference in distribution ofinside/out penetration population to outside/in penetration population.A high limit point is 95% of the I/O population for the force anddisplacement while 100% efficiency point for work.

In-vivo, the delivery tool 20 provides an offset needed to increase thelength of the tine that reaches maximum peak force of the deployment(dDFmax) to achieve displacement needed to penetrate endocardial layer.The user or operator of the delivery tool 20 can maintain control of thedelivery by tactile feedback.

The length of the tine that reaches maximum peak force of deployment(dDFmax) and length of the tine that reaches maximum peak force of theretraction (dRFmax) is considered equivalent about equivalent. Thisbalances the mechanism at retraction and deployment. dRFmax is definedas the length of the tine that reaches the end of the force plateau(i.e. typically maximum peak force) of the retraction process.

The length balance provides a safety advantage by minimizing the lengthof the tine in contact with the tissue at retraction. The length of thetine in contact with the tissue at retraction limits the potentialenergy resisting tissue at the retraction of the fixation mechanism.Observing the distribution of the O/I tissue penetration length neededto reach the maxim peak force of penetration, length of the tine thatreaches maximum peak force of the retraction (dRFmax) should be lessthan 95% of the population.

FIG. 4 is a flow diagram illustrating a method of determiningcharacteristics of a set of tines employing an analytical methodaccording to the invention. A computer with a graphical user interfaceor display is used to determine the characteristics of the tines. Inputs300, 302, 304, 306, are received by the processor of the computer foranalysis. Block 300 is the effective cross-sectional area of the tine,which is calculated using the first transfer function, provided below.The confidence level input is provided as input 302. The confidencelevel input is defined by the user. A high confidence level is selectedthat perforations will not occur. For example, a user may select a 95%confidence level that no perforations occur. A high and low limit isselected in which that assess damage to the tissue. Other exemplaryinputs 304, 306 for design parameters (also referred to as tinecharacteristics) include width of the tine, thickness of the tine,radius of a curve for the tine, length of the straight section.Additional or alternative embodiments for design parameters includefixation mechanism material properties, implant medium materialproperties (i.e. tissue properties), desired confidence level, desiredreliability level, use conditions, fatigue performance, etc.

In one preferred embodiment, a 95% or more (e.g. 100%) efficiency isdisplayed to the user at block 310 which indicates that the set of tinesdo not dislodge while a high confidence level at block 312 is selectedthat perforations will not occur. Additionally or alternatively, otherdata can be displayed to the user such as performance level (i.e.holding force-displacement-energy), projection of reliability boundsover time. Blocks 310, and 312 are not calculated using the firsttransfer function. Rather, these are limits that assist in determiningthe tines characteristics which are displayed at block 314.

FIG. 10 is a flow chart depicting how to form tines for a lead 22. Atblock 402, the cross-sectional area of the distal end of the tine isselected. Once the cross-sectional area of the distal end of the tinehas been selected, the effective cross-sectional area of the tine isdetermined by using the first transfer function. The exemplary firsttransfer function is as follows:

Wintg(J)(Chamberlain Group Part Number 1361)=0.0063×Agp_ecs(mm²)−0.0004  Transfer Function 1

Effective cross-sectional area (Agp_ecs (mm²)) is the area of thepenetrator tip in contact with the tissue referenced to a standard (i.e.the flat bottom cylinder gauge pin). The tissue, in which the tines 24will be attached thereto, is tested to determine the high and low levelamount of energy that will potentially cause damage to the tissue. Forexample, assume the right ventricular tissue is to be tested the energyand the displacement associated with the energy are calculated throughthe first transfer function. The effective cross-sectional area for thedistal end of the tine is plugged into the high and low level transferfunctions.

The high and low level limits that assess damage to the tissue areprovided by the following transfer functions:

Wintg(J)=1.339E-02×Agp_ecs (mm2)−6.984E-04 R²=0.963

High level limit transfer function

The low level limit is provided by the following transfer function:

Regression equation for the biggest percent-difference IO to OI of thedisplacement d (mm):

Wintg(J)=1.339E-02×Agp_ecs (mm2)−6.984E-04 R²=0.963

Displacement (d (mm)) refers to the depth of material tented under theload applied by the penetrator of known effective cross-sectional area.The distance the penetrator has traveled to displace tissue beforeentering the tissue.

FIGS. 11A-11D show a process for deploying the set of tines in the rightatrial appendage (RAA). FIG. 11A depicts a schematic view of the initialimplant stage in which the delivery system 20, including the lead, ispositioned near the RAA while the tines are retracted to avoid snaggingthe tines on any anatomical areas. The distal end of the delivery system20 directly faces the pectinate muscle and has not contacted theepicardial layer of the heart. While moving the delivery system 20, thephysician employs an imaging system such as fluoroscopy in order toposition the delivery system in pectinate structure.

FIG. 11 B depicts the delivery system being placed or pushed in theappendage to the desired target location. Once the physician beginspushing on the lead 20, the effective length of the tine inside theheart is changing because the lead is exiting delivery system 20.Delivery system 20 configured to be soft or flexible and is opposing thereaction force of the tines. Thus, the delivery system 20 is applying alimiting force that can be applied to the tissue by the delivery system20 thereby deflecting back. The delivery system in combination with thelead designed with tines is an improvement over conventional deliverysystems. For example, one type of conventional delivery system 20 isextremely rigid and the lead is also very rigid. The combination of theconventional delivery system and the lead would not move. Consequently,the resulting pressure from the stiff delivery system and lead wouldforce the tines through the heart wall in contrast to the deliverysystem 20 of the present disclosure.

FIG. 11C depicts a schematic view of the delivery system during theprocess of deploying the tines. The tines penetrate the pectinate muscleand reached the tougher endocardial layer. The delivery system energybalance with tissue energy when only the pectinate muscle is penetratedby the tines. The tines can pierce the pectinate muscle and contact theepicaridal surface. The tines can move along side the epicardialsurface.

FIG. 11D depicts a schematic view of the delivery system in which a“kick back” force causes the delivery system to move in a backwardmotion from its position. In response to the “kick back”, the tinescontact the epicardial surface.

FIG. 11E depicts a schematic view of the delivery system such that whenthe tines contact the epicardial surface, the delivery system (i.e.catheter) column strength was not sufficiently stiff to allow tines topenetrate tougher layers. The delivery system “kicks back” and therebylimits the tip force. The tines are then completely deployed.

FIGS. 12A-12B depict a delivery system (or delivery catheter) that canonly provide enough reaction force to penetrate the pectinate layer ofthe RAA. As shown, the tines are angled toward the target tissue (e.g.RAA) which is achieved by the delivery system bending and pivoting dueto the flexibility in the delivery system (i.e. catheter). FIG. 12Adepicts a delivery system 20 in which the distal end of the deliverysystem is angled toward the target tissue site. FIG. 12B depicts adelivery system 20 in which the tines on the lead are attached to thetissue at an angle while the delivery system is bending and pivoting.

FIGS. 13A-13-D illustrate of the straight section of the tine-tissueinterface during initial penetration of the endocardial surface. A forceis applied to the tine tip, which displaces the tissue (i.e. tenting)and generates pressure (FIG. 13A and FIG. 13B). As the tine movesforward and the tissue continues to displace, the pressure increases tothe point at which the tine penetrates the tissue (FIG. 13C). Once thetissue is penetrated, the pressure is relieved and the tissue returns toits native position (FIG. 13D).

Lead 22 can be implanted in many different locations in the heart. Forexample, lead 22 can be placed inside the right atrium or rightventricle. The acute perforation properties of the right atrialappendage (RAA) were determined to provide superior results with respectto fixation to the tissue while exhibiting limited perforations of thethinly-walled right atrium.

Estimated rates of acute pacemaker lead perforations range between0.5-2%, establishing significant clinical and device designconsiderations. Although pericardial effusion may result fromperforation and can be a significant clinical issue, limited researchhas investigated the biomechanical properties of atrial tissue. A studywas performed to better define the relationship between perforationforces of the right atrial appendage (RAA) and the surface areas of theapplied penetrating devices (e.g. a lead or fixation mechanism).

For this study, to date, the RAA was dissected from swine (n=10) andhuman (n=1) donor hearts and secured in a custom chamber. An oxygenatedKrebs-Henseleit buffer promoted tissue viability, and maintained tissuetemperature at 37° C.

Cylindrical penetrators diameters between diameter=0.25-12.7 mm werequasi-statically advanced at 120 mm/min until perforation occurred.Quasi-static means that the motion during the perforation is so slowthat no dynamic effects occur.

Perforation forces of pectinate muscle and the epicardium of the RAAwere investigated (swine, n=280 penetrations; human, n=40 penetrations).

The perforation forces (F_(P): Newtons) vary linearly with penetratorcross-sectional area (CSA: mm²) for both pectinate muscle (swine,F_(P)=0.97*CSA+0.28, R²=0.54; human, F_(P)=3.14*CSA+0.23, R²=0.16) andepicardium of the RAA (swine, F_(P)=1.62*CSA−0.63, R²=0.58; human,F_(P)=6.62*CSA+0.61, R²=0.22). F_(p) for epicardial tissue wassignificantly higher than F_(p) for pectinate muscle for all penetrators(p<0.05). Perforations of lateral wall pectinate required greater forcesthan perforations of the distal tips of the RAA (95% CI for slope [1.01,1.34] vs [0.63, 0.82]). Perforations of the epicardial layer withinvarious anatomical RAA locations required no significant difference inforce.

The present disclosure provides one or more approaches to assessperforation properties within the RAA of both human and swine hearts. Westudied both pectinated and thin walled regions in multiple anatomicallocations within the RAA. This biomechanical information can optimizethe design and implementation of novel atrial fixation technologies.

The set of tines can be secured to a variety of medical electricalleads. FIGS. 5-8 depict a schematic view of a medical electrical lead 22with a set of tines at a distal end of the lead 22. Lead 22 can beconfigured from a variety of lead bodies. Exemplary leads fitted withthe crown (shown in ghost lines in FIG. 8) in which set of tinesextending therefrom can be the CAPSURE SENSE® 4074 commerciallyavailable from Medtronic, Inc., the ISLOFLEX™ commercially availablefrom St Jude Medical, and the INGEVITY™ MRI lead commercially availablefrom Boston Scientific. The manuals for the CAPSURE SENSE® 4074,ISLOFLEX™ and the INGEVITY™ MRI lead are incorporated by reference intheir entirety. Skilled artisans understand that set of tines can beconfigured to be secured to any lead as long as the design requirementsset forth herein are met.

Lead 22 includes an elongated lead body 17 that extends from a proximalend to a distal end. The lead body 17 can include one or more jacketedelongated conductive elements. A jacket (also referred to as a layer,longitudinal element, coating) extends along and longitudinally aroundthe conductive elements and serves to insulate one or more conductiveelements.

Electrically conductive elements for lead 22 can include coils, wires,coil wound around a filament, cables, conductors or other suitablemembers. Conductive elements can comprise platinum, platinum alloys,titanium, titanium alloys, tantalum, tantalum alloys, cobalt alloys(e.g. MP35N, a nickel-cobalt alloy etc.), copper alloys, silver alloys,gold, silver, stainless steel, magnesium-nickel alloys, palladium,palladium alloys or other suitable materials. Electrically conductiveelement is covered, or substantially covered, longitudinally with ajacket (also referred to as a layer, a longitudinal element, alongitudinal member, a coating, a tubular element, a tube or acylindrical element). Typically, the outer surface of electrodes such asthe ring electrode, the tip electrode, and the defibrillation coils areexposed or not covered by a jacket or layer so that electrodes can senseand/or deliver electrical stimuli to tissue of a patient.

Active fixation mechanisms such as the tines, are located at the distalend 44 of lead 22. Optionally, one or more of the electrodes, can bedrug eluting such as that which is disclosed in US 20140005762 filedJun. 29, 2012, assigned to the assignee of the present invention, isincorporated by reference in its entirety. As shown, the electrode 42(i.e. serving as an anode) is located proximal to the tines 24 and thetip electrode 46 (i.e. serving as a cathode). Additionally, the tip andring electrodes can be coated with titanium nitride (TiN).

Exemplary liners for lead 22 that can be used in conjunction with thepresent disclosure are shown and described with respect to U.S. Pat. No.8,005,549 issued Aug. 23, 2011, U.S. Pat. No. 7,783,365 issued Aug. 24,2010, and assigned to the assignee of the present invention, thedisclosure of which are incorporated by reference in their entiretyherein. ATTAIN PERFORMA™ Model 4298 quadripolar lead insulation isanother exemplary insulative material that can be used. Examples ofconnector modules may be seen with respect to U.S. Pat. No. 7,601,033issued Oct. 13, 2009, U.S. Pat. No. 7,654,843 issued Feb. 2, 2010, andassigned to the assignee of the present invention, the disclosure ofwhich are incorporated by reference in their entirety herein. Theconnector module can take the form of an IS-4 bipolar connecter, but anyappropriate connector mechanism may be substituted. Connector module 14electrically couples a proximal end of each lead to various internalelectrical components of implantable medical device 10 through aconnector or set screw.

Performance of the tines achieved the prespecified conditions set forthherein. The tines were evaluated relative to attachment to tissue ortissue-like conditions. The intersection of the tissue conditionsperformance region and the performance population distributions definesa successful fit of the prototypes of the tines.

Specifically, effective cross-sectional area characteristic of thedistal end of each tine fell between a high limit point regression lineand low limit point regression line. The tines satisfied tissue useconditions when the resultant data fell within the high limit and lowlimit lines intersected.

It should also be noted that leads may also be employed for stimulationof other tissue types besides cardiac tissue. The present invention isbelieved to be adaptable to such uses as well. In such cases, thresholdsfor stimulation for the tissue type and amplitudes of signals sensedfrom the tissue would be substituted for pacing threshold and R-waveamplitude as is appropriate. Additionally, other measured parameters ofthe other tissue types may be substituted for those discussed above ormay be used in addition to those discussed above.

The present disclosure includes the following embodiments:

-   Embodiment 1 is a system for implantation of a lead medical    electrical lead in contact with heart tissue, comprising:

an elongated lead body;

a set of curved tines mounted to and extending from a distal end of thelead body, the tines having a length (dD) and an effective crosssectional area;

a delivery catheter, enclosing the lead body and having a distal capsuleportion enclosing the tines, the tines exerting a spring force againstthe capsule and providing a stored potential energy, the deliverycatheter having an ejection means for advancing the lead and tinesdistally from the capsule and fixating the tines within the hearttissue, the ejection means and the stored potential energy of the tinestogether providing a deployment energy, the tines when so fixated in thetissue providing a fixation energy; and

wherein the deployment energy and the fixation energy are equivalent.

-   Embodiment 2 is system as in embodiment 1, wherein the deployment    energy provides a provides a maximum peak force of deployment    (dDFmax) and the fixation energy provides a maximum peak force of    the retraction (dRFmax) and wherein the length of the tines (dD) is    such that (dDFmax) and (dRFmax) are equivalent.-   Embodiment 3 is the system according to any of embodiments 1 or 2,    wherein (dRFmax) falls between a level sufficient to penetrate the    heart tissue from an epicardial surface thereof (O/I) and a level    sufficient to penetrate the heart tissue from an endocardial surface    thereof (O/I).-   Embodiment 4 is a system according to any of embodiments 1-3 wherein    the potential energy provided by the spring force of the tines    against the capsule is less than the fixation energy.-   Embodiment 5 is a system for implantation of a lead medical device    in contact with heart tissue, comprising:

a medical device;

a set of curved tines mounted to and extending from a distal end of thedevice, the tines having a length (dD) and an effective cross sectionalarea;

a delivery catheter, enclosing the device and having a distal capsuleportion enclosing the tines, the tines exerting a spring force againstthe capsule and providing a stored potential energy, the deliverycatheter having an ejection means for advancing the tines distally fromthe capsule and fixating the tines within the heart tissue, the ejectionmeans and the stored potential energy of the tines together providing adeployment energy, the tines when so fixated in the tissue providing afixation energy; and

wherein the deployment energy and the fixation energy are equivalent.

-   Embodiment 6 is a system as in embodiment 5, wherein the deployment    energy provides a provides a maximum peak force of deployment    (dDFmax) and the fixation energy provides a maximum peak force of    the retraction (dRFmax) and wherein the length of the tines (dD) is    such that (dDFmax) and (dRFmax) are equivalent.-   Embodiment 7 is a system according to any of embodiments 5 or 6,    wherein (dRFmax) falls between a level sufficient to penetrate the    heart tissue from an epicardial surface thereof (O/I) and a level    sufficient to penetrate the heart tissue from an endocardial surface    thereof (O/I).-   Embodiment 8 is a system according to any of embodiments 5-7 wherein    the potential energy provided by the spring force of the tines    against the capsule is less than the fixation energy.-   Embodiment 9 is a system according to any of embodiments 5-8 wherein    the device is a medical electrical lead comprising an elongated lead    body and wherein the tines are mounted to a distal end of the lead    body.-   Embodiment 10 is a method of making a medical electrical lead type    having a set of tines, the method comprising:

determining effective cross-sectional area characteristic of a distalend of each tine in the set of tines relative to a displacement energyrequired to displace a set of tissue layers;

in response to determining the effective cross-sectional areacharacteristic of the distal end of each tine, determining whether asubstantially high confidence level characteristic exists thatperforation is avoided; and

making the set of tines in which each tine exhibits the determinedcharacteristics.

-   Embodiment 11 is a method according to embodiment 10 wherein a    transfer function associates effective cross-sectional area of a    distal end of each tine in the set of tines to the displacement    energy.-   Embodiment 12 is a method according to embodiment 11 wherein the    high confidence level is determined based upon 100% efficiency of    the set of tines staying in position without dislodging.-   Embodiment 13 is a method according to any of embodiments 11-12    comprising configuring the set of times to solely penetrate viable    tissue in response to determining the transfer function.-   Embodiment 14 is a method according to any of embodiments 10-13    wherein the set of tines are configured to not penetrate veins.-   Embodiment 15 is a method according to any of embodiments 10-14    wherein the set of tines are configured to not penetrate arteries.-   Embodiment 16 is a method according to any of embodiment 10-15    wherein the set of tines are configured to not penetrate non-viable    cardiac tissue.-   Embodiment 17 is a method according to any of embodiments 10-16    wherein a transfer function associates effective cross-sectional    area of a distal end of each tine in the set of tines to the    work/energy.-   Embodiment 18 is a method according to embodiment 17 wherein the    determining step comprises application of the transfer function    derived from testing of leads of the type.-   Embodiment 19 is a method according to any of embodiments 17-18    wherein the displacement energy is defined by a peak maximum force    and associated displacement.-   Embodiment 20 is a method according to any of embodiments 10-19    wherein the tissue is heart tissue.-   Embodiment 21 is a method according to any of embodiments 10-20    wherein the tines are configured to provide 100% efficiency of    fixation for 95% of a population in which the lead may be implanted.-   Embodiment 22 is a method according to any of embodiments 10-21    further comprising selecting a high level point and a low level    point to achieve a 100% efficiency of fixation for the 95% of the    population.-   Embodiment 23 is a method according to any of embodiments 10-22    wherein the tines are configured to provide at least 95% efficiency    of fixation for 95% of a population in which the lead may be    implanted.-   Embodiment 24 is a method according to any of embodiments 10-23    further comprising selecting a high level point and a low level    point to achieve at least 95% efficiency of fixation for the 95% of    the population.-   Embodiment 25 is a method according to any of embodiments 10-24    wherein the set of tines comprises three or more tines.

Embodiment 26 is a system for implantation of a lead medical electricallead in contact with heart tissue, comprising:

an elongated lead body;

a set of curved tines mounted to and extending from a distal end of thelead body, the tines having a length (dD) and an effective crosssectional area;

a delivery catheter, enclosing the lead body and having a distal capsuleportion enclosing the tines, the tines exerting a spring force againstthe capsule and providing a stored potential energy, the deliverycatheter having an pushing means for advancing the lead and tinesdistally from the capsule and fixating the tines within the hearttissue, the pushing means and the stored potential energy of the tinestogether providing a deployment energy, the tines when so fixated in thetissue providing a fixation energy; and

wherein the deployment energy and the fixation energy are equivalent.

-   Embodiment 27 is a system of embodiment 26 wherein the pushing means    is one of a stylet, a guidewire and a hybrid stylet/guidewire.-   Embodiment 28 contemplates that the delivery system and medical    electrical lead should provide 0.5 Newtons-0.3*(0.5 Newtons)of force    and/or energy.

The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousmodifications and alterations to this disclosure will become apparent tothose skilled in the art without departing from the scope and spirit ofthis disclosure. It should be understood that this disclosure is notintended to be unduly limited by the illustrative embodiments andexamples set forth herein and that such examples and embodiments arepresented by way of example only with the scope of the disclosureintended to be limited only by the claims set forth herein as follows.

1. A system for implantation of a lead medical electrical lead incontact with heart tissue, comprising: an elongated lead body; a set ofcurved tines mounted to and extending from a distal end of the leadbody, the tines having a length (dD) and an effective cross sectionalarea; a delivery catheter, enclosing the lead body and having a distalcapsule portion enclosing the tines, the tines exerting a spring forceagainst the capsule and providing a stored potential energy, thedelivery catheter having an ejection means for advancing the lead andtines distally from the capsule and fixating the tines within the hearttissue, the ejection means and the stored potential energy of the tinestogether providing a deployment energy, the tines when so fixated in thetissue providing a fixation energy; and wherein the deployment energyand the fixation energy are equivalent.
 2. A system as in claim 1,wherein the deployment energy provides a provides a maximum peak forceof deployment (dDFmax) and the fixation energy provides a maximum peakforce of the retraction (dRFmax) and wherein the length of the tines(dD) is such that (dDFmax) and (dRFmax) are equivalent.
 3. A system asin claim 2, wherein (dRFmax) falls between a level sufficient topenetrate the heart tissue from an epicardial surface thereof (O/I) anda level sufficient to penetrate the heart tissue from an endocardialsurface thereof (O/I).
 4. A system according to claim 1 wherein thepotential energy provided by the spring force of the tines against thecapsule is less than the fixation energy.
 5. A system for implantationof a lead medical device in contact with heart tissue, comprising: amedical device; a set of curved tines mounted to and extending from adistal end of the device, the tines having a length (dD) and aneffective cross sectional area; a delivery catheter, enclosing thedevice and having a distal capsule portion enclosing the tines, thetines exerting a spring force against the capsule and providing a storedpotential energy, the delivery catheter having an ejection means foradvancing the tines distally from the capsule and fixating the tineswithin the heart tissue, the ejection means and the stored potentialenergy of the tines together providing a deployment energy, the tineswhen so fixated in the tissue providing a fixation energy; and whereinthe deployment energy and the fixation energy are equivalent.
 6. Asystem as in claim 5, wherein the deployment energy provides a providesa maximum peak force of deployment (dDFmax) and the fixation energyprovides a maximum peak force of the retraction (dRFmax) and wherein thelength of the tines (dD) is such that (dDFmax) and (dRFmax) areequivalent.
 7. A system as in claim 5, wherein (dRFmax) falls between alevel sufficient to penetrate the heart tissue from an epicardialsurface thereof (O/I) and a level sufficient to penetrate the hearttissue from an endocardial surface thereof (O/I).
 8. A system accordingto claim 5 wherein the potential energy provided by the spring force ofthe tines against the capsule is less than the fixation energy.
 9. Asystem according to claim 5 wherein the device is a medical electricallead comprising an elongated lead body and wherein the tines are mountedto a distal end of the lead body.
 10. A method of making a medicalelectrical lead type having a set of tines, the method comprising:determining effective cross-sectional area characteristic of a distalend of each tine in the set of tines relative to a displacement energyrequired to displace a set of tissue layers; in response to determiningthe effective cross-sectional area characteristic of the distal end ofeach tine, determining whether a substantially high confidence levelcharacteristic exists that perforation is avoided; and making the set oftines in which each tine exhibits the determined characteristics.
 11. Amethod according to claim 10 wherein a transfer function associateseffective cross-sectional area of a distal end of each tine in the setof tines to the displacement energy.
 12. A method according to claim 11wherein the high confidence level is determined based upon 100%efficiency of the set of tines staying in position without dislodging.13. A method according to claim 11 comprising configuring the set oftimes to solely penetrate viable tissue in response to determining thetransfer function.
 14. A method according to claim 10 wherein the set oftines are configured to not penetrate veins.
 15. A method according toclaim 10 wherein the set of tines are configured to not penetratearteries.
 16. A method according to any of claim 10 wherein the set oftines are configured to not penetrate non-viable cardiac tissue.
 17. Amethod according to claim 10 wherein a transfer function associateseffective cross-sectional area of a distal end of each tine in the setof tines to the work/energy.
 18. A method according to claim 17 whereinthe determining step comprises application of the transfer functionderived from testing of leads of the type.
 19. A method according toclaim 17 wherein the displacement energy is defined by a peak maximumforce and associated displacement.
 20. A method according to any ofclaim 10 wherein the tissue is heart tissue.
 21. A method according toclaim 10 wherein the tines are configured to provide 100% efficiency offixation for 95% of a population in which the lead may be implanted. 22.A method according to claim 10 further comprising selecting a high levelpoint and a low level point to achieve a 100% efficiency of fixation forthe 95% of the population.
 23. A method according to claim 10 whereinthe tines are configured to provide at least 95% efficiency of fixationfor 95% of a population in which the lead may be implanted.
 24. A methodaccording to claim 10 further comprising selecting a high level pointand a low level point to achieve at least 95% efficiency of fixation forthe 95% of the population.
 25. A method according to claim 10 whereinthe set of tines comprises three or more tines.
 26. A system forimplantation of a lead medical electrical lead in contact with hearttissue, comprising: an elongated lead body; a set of curved tinesmounted to and extending from a distal end of the lead body, the tineshaving a length (dD) and an effective cross sectional area; a deliverycatheter, enclosing the lead body and having a distal capsule portionenclosing the tines, the tines exerting a spring force against thecapsule and providing a stored potential energy, the delivery catheterhaving an pushing means for advancing the lead and tines distally fromthe capsule and fixating the tines within the heart tissue, the pushingmeans and the stored potential energy of the tines together providing adeployment energy, the tines when so fixated in the tissue providing afixation energy; and wherein the deployment energy and the fixationenergy are equivalent.
 27. A system of claim 26 wherein the pushingmeans is one of a stylet, a guidewire and a hybrid stylet/guidewire.